The teams completed the surprising trade Wednesday night. Walker was considered one of the top young pitchers in the American League, but struggled with consistency. Yet he's shown flashes of having the potential to become an ace during his young career. Marte had many of the same problems with consistency but had also become a liability in the field.

Walker, 24, was 8-11 with a 4.22 ERA and 119 strikeouts in 25 starts last season.

Segura is an immediate upgrade at shortstop for Seattle. He hit .319 with 20 home runs and 63 RBIs last season for the Diamondbacks and will provide Seattle with a legitimate leadoff hitter. Arizona also sent outfielder Mitch Haniger and left-handed pitcher Zac Curtis to Seattle.